This application claims priority from Canadian Patent Application No. 2,364,401, filed on Dec. 5, 2001 which is hereby incorporated herein by reference.
The invention pertains to the field of inkjet printing and, in particular, to the maintenance of inkjet printheads.
Drop-on-demand or continuous-stream inkjet printers, such as thermal, piezoelectric, acoustic, or phase change wax-based printers, have at least one printhead from which droplets of ink are directed towards a printing medium (or substrate). Within such printheads, ink is typically contained in a plurality of channels. By means of power pulses, droplets of ink are expelled as required from orifices or nozzles at the end of these channels. The mechanisms whereby ink ejection works in these various types of machines are well established and will not be further discussed herein.
An inkjet printhead may be incorporated into a carriage type printer, a partial width array type printer, or a pagewide type printer. A carriage type printer typically has a relatively small printhead containing a number of ink channels and nozzles. The printhead can be attached to a disposable ink supply cartridge and the combined printhead and cartridge assembly is attached to a carriage. The carriage is reciprocated to print one swath of information (having a height equal to the length of a column of nozzles) at a time on a recording medium, which is typically maintained in a stationary position during the reciprocation. After the swath is printed, the paper is stepped a distance equal to the height of the printed swath or a portion thereof, so that the next printed swath is contiguous or overlapping therewith. Overlapping is often employed to address a variety of undesirable inkjet printing artifacts that may be traced to nozzle performance. This procedure is repeated until the entire page is printed.
In contrast, a pagewide printer includes a substantially stationary printhead having a length sufficient to print across the width or length of a sheet of printing medium. The printing medium is continually moved relative to the pagewide printhead in a direction which may be substantially normal to the printhead length. In most cases, the separation between individual nozzles is greater than the required dot spacing on the media, and hence the media may be passed under the pagewide printhead more than once in order to print at the interstitial positions or to address a variety of undesirable inkjet printing artifacts that may be traced to nozzle performance.
There is a need to maintain the ink-ejecting nozzles of an inkjet printhead. For example, the orifices typically need to be cleaned periodically and/or the printhead needs to be capped when the printer is out of use or is idle for an extended period. Capping the printhead prevents components of the ink in the printhead from evaporating and prevents contaminants from entering the printhead or contaminating the nozzle plate. There is sometimes a need to prime a printhead before use. This is done to insure that the printhead channels are completely filled with ink and contain no contaminants or air bubbles. Periodic priming may also be necessary to maintain proper functioning of the orifices. Maintenance and/or priming stations for the printheads of various types of inkjet printers are described for example, in U.S. Pat. Nos. 4,855,764, 4,853,717, and 4,746,938.
Various methods and apparatus for maintaining the condition of inkjet printheads are generally known in the art, as illustrated and described in the following references.
U.S. Pat. No. 5,206,666 to Watanabe et al., describes an inkjet recording apparatus having a full-line type recording head that is rotated between a recording position and a non-recording position. A cleaning member contacts the recording head during rotation of the recording head to remove deposited ink or foreign matter. In the non-recording position, the printhead is capped.
U.S. Pat. No. 5,257,044 to Carlotta et al., describes a cap actuation mechanism for an inkjet printhead maintenance station in a scanning type inkjet printer. A cap located on a cap carriage in the maintenance station provides the functions of printhead nozzle capping, priming, cleaning, and refreshing, as well as waste ink management.
U.S. Pat. No. 5,367,326 to Pond et al., describes a pagewide inkjet printer having a movable cleaning/priming station adapted for movement parallel to and along an array of printhead nozzles. The cleaning and priming station is slid along a ledge surface so that the cleaning and priming station is maintained a fixed distance from the face of the printhead.
A number of proposals suggest the use of media sheets for cleaning and maintaining inkjet printheads. For example, Japanese patent application JP 4141439A2 discloses a method for cleaning a printhead by pressing paper travelling through a printer against the printhead. Similarly, U.S. Pat. No. 4,947,190 suggests the use of an ink-absorbing cleaning sheet that is brought into contact with the printhead in order to wipe and clean the printhead. Other proposals for cleaning sheets have included sheets with specified surface roughnesses, adhesives, or absorbent or solvent-soaked pads (e.g., see U.S. Pat. No. 6,030,674, U.S. Pat. No. 5,589,865, U.S. Pat. No. 6,277,457, U.S. Pat. No. 5,751,306, U.S. Pat. No. 5,589,865).
Because media sheets work by coming into physical contact with the nozzle orifice plate, they can be made suitable for operations such as wiping off ink or debris or applying solvent. However, care must be taken to ensure that:
contact with the orifice plate does not abrade or otherwise damage the surface;
the action of the media sheet, or debris from the sheet itself, does not contribute to the clogging of nozzle orifices; and,
the media sheet makes adequate contact with the surface to be cleaned.
Media sheets can be transported past the inkjet printhead along the existing media carrier path. However, it should be noted that rubbing and wiping printhead surfaces alone does not address all of the maintenance needs associated with inkjet printheads. Additional mechanisms for capping, priming, spitting, and/or suctioning the printheads will still be required for adequate maintenance. This requirement is reflected in U.S. Pat. No. 5,589,865, which discloses a cleaning sheet which has an opening in order to allow the passage of a separate vacuum wand.
As the technology has developed for fabricating ever higher resolution inkjet heads with ever greater densities of nozzles, and, more particularly, with the advent of pagewide systems, the requirements placed on maintenance systems have become even more complex. A typical maintenance system may include one or more of:
a cap assembly to seal around an individual printhead or nozzle plate to keep the particular inkjet nozzle array from drying out and the nozzle plate free from contaminants;
a wiper that can be moved to engage the nozzle surface of the printhead and clear away ink, debris and other undesirable matter from the surface of the nozzle plate area, and which may be moved away from the nozzle surface when wiping is not desired;
a spittoon for receiving ink ejected from the nozzles to remove contaminated ink from the nozzles and to maintain less used nozzles;
a selection of drive assemblies that may include a gear train for moving the cap, wiper and/or a spittoon;
an absorption pad for absorbing drops of ink ejected during maintenance so that the printer may be transported without damaging or soiling parts of the printer with purged ink; and,
a mechanism for cleaning the cap and wiper to prevent contaminants being transported onto the nozzle plate during successive maintenance procedures.
An inkjet printhead maintenance system can be a complex subsystem with many moving parts.
U.S. Pat. No. 6,179,403 to Xie describes a drum-based inkjet printing apparatus that includes a maintenance system located at one end of the print drum. The maintenance system includes assemblies that provide wet wiping of the nozzles of the printheads as well as vacuuming of the same printheads for maintenance thereof. The wet wipe nozzles are located within a stationary drum housing and extend through a plurality of apertures when necessary to provide maintenance functions. The printhead is mounted on a carriage which moves to the maintenance position, where the wet wipers apply a fluid to the inkjet nozzles such that any dried ink, viscous plugs or other debris is loosened on the front face of the inkjet printbars. Once the debris has been sufficiently loosened, a plurality of vacuum nozzles each extending through a plurality of vacuum nozzle apertures vacuum away any of the cleaning fluid as well as debris loosened thereby.
Other examples are known in the art, where a pad is attached to an extra-wide cylinder and the printhead is translated over a long distance to clear the nozzles over this pad.
While this approach addresses some of the requirements enumerated above, it nevertheless still requires the entire high precision printhead to be translated over a considerable distance to a service/maintenance position.
A maintenance system for an inkjet printhead assembly is relocated to the location of the inkjet printhead assembly to maintain the inkjet printhead assembly. The relocation is performed by temporarily attaching the maintenance station to the media carrier of the inkjet printer. The printing media carrier may also be moved to place the maintenance system in a position where it may itself be serviced by a docking station.
Further aspects of the invention and features of specific embodiments of the invention are described below.